TCE Biology Level 3: Ecosystems & Sustainability — Flashcards & Quiz

Q1: Define ecosystem, community, population and habitat.

An ecosystem is a community of living organisms (biotic) interacting with their non-living environment (abiotic). A community is all the populations of different species living in the same area. A population is a group of individuals of the same species in a given area. A habitat is the physical place where an organism lives, characterised by specific abiotic and biotic factors.

Q2: Explain the difference between a food chain and a food web.

A food chain is a linear sequence showing the transfer of energy from one organism to the next (producer → primary consumer → secondary consumer → tertiary consumer). A food web is a network of interconnected food chains showing all feeding relationships in an ecosystem. Food webs are more realistic because most organisms feed on multiple species.

Q3: What are trophic levels and why are there usually only 4-5 levels in a food chain?

Trophic levels are the feeding positions in a food chain: Level 1 (producers/autotrophs), Level 2 (primary consumers/herbivores), Level 3 (secondary consumers/carnivores), Level 4 (tertiary consumers/apex predators). There are usually only 4-5 levels because only about 10% of energy is transferred between each level — the rest is lost as heat through respiration, excretion and decomposition. Insufficient energy remains to support higher levels.

Q4: Explain why energy flow in an ecosystem is described as one-way and non-cyclical.

Energy enters ecosystems as sunlight, is converted to chemical energy by photosynthesis, and passes through trophic levels. At each level, most energy (~90%) is lost as heat through cellular respiration and is unavailable to higher levels. Energy cannot be recycled — it must be continuously supplied by the sun. This contrasts with nutrients, which are recycled.

Q5: Outline the carbon cycle.

Carbon enters living systems when producers fix atmospheric CO₂ via photosynthesis into organic compounds (glucose). Carbon passes through food chains as organisms consume each other. Carbon returns to the atmosphere through: cellular respiration (CO₂), decomposition of dead organisms, combustion of fossil fuels and volcanic activity. Carbon is also stored long-term in fossil fuels, limestone, ocean sediments and biomass.

Q6: Outline the nitrogen cycle.

Nitrogen cycle: 1) Nitrogen fixation — N₂ converted to NH₃ by nitrogen-fixing bacteria (Rhizobium in legume root nodules) or lightning. 2) Nitrification — NH₃ converted to NO₂⁻ then NO₃⁻ by nitrifying bacteria (Nitrosomonas, Nitrobacter). 3) Assimilation — plants absorb NO₃⁻ to make amino acids and proteins. 4) Ammonification — decomposers break down dead organisms, releasing NH₃. 5) Denitrification — denitrifying bacteria convert NO₃⁻ back to N₂ (in anaerobic conditions).

Q7: Outline the phosphorus cycle and explain why it differs from carbon and nitrogen cycles.

The phosphorus cycle has no atmospheric component — phosphorus cycles between rock, soil, water and organisms. Weathering of phosphate-containing rocks releases PO₄³⁻ into soil and water. Plants absorb phosphate from soil; animals obtain it by eating plants. Decomposers return phosphorus to the soil. Phosphorus also accumulates in ocean sediments and may take millions of years to return to the cycle via geological uplift.

Q8: Describe exponential and logistic population growth models.

Exponential growth (J-curve): population grows without limits when resources are abundant — Nt = N₀e^(rt). Growth rate is constant and population increases rapidly. Logistic growth (S-curve): population growth slows as it approaches the carrying capacity (K) due to increasing competition for limited resources — the growth rate decreases as N approaches K. The population stabilises near K.

Q1: An ecosystem includes both biotic (living) and abiotic (non-living) components.

Answer: TRUE

An ecosystem is defined as a community of living organisms (biotic) interacting with their physical and chemical environment (abiotic factors such as temperature, water, light and soil).

Q2: A food web is a single linear pathway showing energy transfer from producer to top consumer.

Answer: FALSE

A FOOD CHAIN is a single linear pathway. A food WEB is a network of interconnected food chains showing all feeding relationships in an ecosystem.

Q3: Approximately 10% of energy is transferred from one trophic level to the next.

Answer: TRUE

The 10% rule states that only about 10% of energy at one trophic level is passed to the next — the rest is lost as heat through respiration, excretion and decomposition.

Q4: Energy in an ecosystem is recycled between trophic levels by decomposers.

Answer: FALSE

NUTRIENTS are recycled by decomposers, but ENERGY flows one way and is ultimately lost as heat. Energy cannot be recycled — it must be continuously supplied by the sun through photosynthesis.

Q5: The carbon cycle includes both photosynthesis (removing CO₂) and respiration (releasing CO₂).

Answer: TRUE

Photosynthesis removes CO₂ from the atmosphere and fixes it into organic molecules. Respiration by all living organisms releases CO₂ back to the atmosphere. Both are essential parts of the carbon cycle.

Energy Flow and Trophic Levels

Energy enters ecosystems through photosynthesis and flows through trophic levels with approximately ten percent efficiency at each transfer. Understanding food webs, energy pyramids, and the implications of energy loss helps you interpret ecological data presented in TASC assessments.

Nutrient Cycling

Carbon, nitrogen, and phosphorus cycles describe how essential elements move through biotic and abiotic components of ecosystems. Being able to trace these cycles and explain how human activities disrupt them is a frequently assessed skill in extended response questions.

Population Ecology

Population growth models, carrying capacity, and limiting factors explain how species populations change over time. Interpreting population graphs and predicting outcomes of environmental changes are practical skills that TASC examiners regularly test.

Biodiversity and Conservation

Biodiversity can be measured at genetic, species, and ecosystem levels. Understanding threats such as habitat loss, invasive species, and climate change, along with conservation strategies like wildlife corridors and captive breeding, prepares you for evaluative questions.

What does TCE Biology Level 3 Ecosystems & Sustainability cover?

This topic covers ecosystem structure and function, food webs and trophic levels, energy flow and ecological pyramids, nutrient cycling (carbon, nitrogen and phosphorus cycles), population ecology and growth models, carrying capacity, interspecific relationships (predation, competition, mutualism, parasitism), conservation biology, human impacts on ecosystems and sustainable management strategies.

How many flashcards are in this set?

This free set contains 20 flashcards and 20 true/false quiz questions covering all key concepts in TCE Biology Level 3 Ecosystems & Sustainability, aligned to the TASC Biology Level 3 course document.

Are these flashcards aligned to the TASC TCE syllabus?

Yes — every flashcard and quiz question is mapped to the TASC Biology Level 3 course content for Ecosystems and Sustainability, ensuring relevance to your external examination and ATAR.